Question

125. Two persons X and Y were caught by policemen at midnight. They had one piece of equipment consisting of a bulb containing acidified K₂Cr₂O₇. By using the equipment policemen could identify that ‘X’ has consumed alcohol and ‘Y’ has not. Explain the principle involved and name the instrument used for the above purpose.

Answer 1

Part 1: Breath analyzer:

• A breath analyzer is a device that is used to estimate blood alcohol concentration in a human body.
• With the help of a breath analyzer, policemen can identify that the person 'X’ has consumed alcohol and ‘Y’ has not.

Part 2: Principle involved in breath analyzer:

• It is based on the principle in which exhaled air is passed through a mixture of sulphuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$, Potassium dichromate $\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$, Silver nitrate, and water $\left({\mathrm{H}}_2\mathrm{O}\right)$.
• In this method, silver nitrate is used as a catalyst, and ethyl alcohol $\left({\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\right)$ in the presence of sulfuric acid turns the Potassium dichromate solution from orange to green due to the conversion of potassium dichromate into chromium sulfate $\left[{\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3\right]$.
• The intensity of the green color indicates the amount of ethyl alcohol in the exhaled air.
• If there is no change in color of potassium dichromate observed, it means that the exhaled air does not have ethyl alcohol.